test: require explicit fetch mocks

packages/core/test/setup.ts

@@ -1,11 +1,6 @@
-// Test setup for Bun test runner
-// This file is loaded before any tests run due to bunfig.toml preload
-
-// Mock fetch globally for tests
-global.fetch =
-  global.fetch ||
-  (() => {
-    throw new Error("fetch is not available in test environment");
-  });
-
-// Add any global test utilities here
+global.fetch = Object.assign(
+  () => {
+    throw new Error("Tests must mock fetch explicitly");
+  },
+  { preconnect: fetch.preconnect },
+) as typeof fetch;